A power distribution system includes a high voltage line used for power distribution of high voltage power, and a low voltage line used for power distribution of low voltage power. A standard voltage and a tolerance range within which a deviation from the standard voltage is allowed are established for these high voltage line and low voltage line. Hence, voltage drop is calculated dividing the power distribution system from a substation to load equipment into a high voltage system including equipment such as the high voltage line and a switch, and a low voltage system including equipment such as the low voltage line and a service drop. After that, the voltage of electric power distributed from the substation is set, or the voltage of power flowing through the power distribution system is adjusted by switching a switch placed in the high voltage system, in such a manner as that the voltages before and after the voltage drop fall within the tolerance range in the high voltage system and the low voltage system.
Patent Document 1: Japanese Laid-open Patent Publication No. 2012-44740
Patent Document 2: Japanese Laid-open Patent Publication No. 2012-29412
However, a reverse flow due to a distributed energy resource or the like is not expected in the above technology. Therefore, the power beyond the tolerance range of voltage may fail to be prevented from flowing in the power distribution system.
In other words, the distributed energy resource is installed at a customer's premises in some cases with the spread of the distributed energy resources such as solar power generation. In this case, a reverse flow may occur from the distributed energy resource installed at the customer's premises to the power distribution system of an electric utility. In this manner, if power flows in two ways between the substation and the load equipment, the change of power at each piece of equipment included in the low voltage system may be increased by the reverse flow. For example, even if the voltage is within the tolerance range during the occurrence of the reverse flow, when the reverse flow stops occurring, power is distributed to the load equipment, which uses the power. Accordingly, the voltage may exceed the tolerance range and be reduced in the power distribution system.